Decorative direct vent fireplace

ABSTRACT

A direct vent fireplace unit that resembles an open hearth wood fireplace. The unit is installable in the interior of a dwelling above a surface defining an outer hearth. The unit includes an outer casing to define a cavity in the dwelling adjacent the outer hearth surface. A combustion chamber is provided having enclosing walls, a floor, a roof and an open front face with a combustion air inlet and an exhaust outlet communicating the combustion chamber with the exterior of the dwelling. The combustion chamber is mountable within the cavity of the outer casing such that the floor of the combustion chamber is substantially co-planar with the surface defining the outer hearth. A burner element for burning fuel within the combustion chamber is connectable to a fuel supply. A controller to control the burner element and a transparent cover mountable over the open front of the combustion chamber to seal the combustion chamber from the interior of the dwelling are also provided. The fireplace unit recreates an open, wood fire ambience with active flames and a large front face for viewing the flames. The unit also enjoys improved heating efficiency over a traditional open fireplace while preserving the preferred active flame appearance.

FIELD OF THE INVENTION

[0001] This invention relates generally to heating appliances and, more particularly, to a fireplace unit that generates heat by burning gas.

BACKGROUND OF THE INVENTION

[0002] Open, wood burning fireplaces are often considered to have the most pleasing appearance among fireplace units by virtue of there being an actual fire consuming fuel in the form of coal or wood. Unfortunately, open, wood burning fireplace are not particularly efficient. With most traditional fireplace designs, only approximately 25% of the heat generated by the fire is used to heat the room, the remainder is lost through the chimney. Open fireplaces also consume heated room air and can adversely affect indoor air quality. There are also potential problems with exhaust flow reversal.

[0003] In response to the above problems with open fireplaces, and, particularly to address the low efficiency aspect of traditional fireplace designs, direct vent heating appliances were developed. Most direct vent heating appliances tend to rely on gas as a fuel and can deliver energy efficiencies approaching 75% of the heat generated being used to heat the room. A direct vent appliance, also known as a “balanced-flue” appliance, is connected directly to the exterior of a building by piping that brings in combustion air and removes exhaust gases. The piping is generally co-linear in the form of two separate runs of piping, or co-axial in which a smaller diameter exhaust pipe is housed concentrically within a larger combustion air pipe. Direct vent appliances are rapidly replacing traditional fireplaces.

[0004] Most popular gas fired direct vent appliances are factory-built units that are retro-fitted into traditional fireplaces or installed in a new location. A common complaint against factory built units is that the fire generated with the units is not realistic. The flame appearance by virtue of direct vent technology, tends to be muted and stagnant bearing little resemblance to a real wood fire. Currently, to achieve the realism of a traditional fireplace using gas, it is necessary to construct a site built masonry fireplace and then purchase and install a factory-built gas log set. Such a project is time consuming, involves several different trades, is very expensive and is ultimately inefficient as the open front design of a traditional fireplace used in conjunction with a gas log set allows large quantities of heated room air to be drawn into the fireplace and sent out of the dwelling with the exhaust from the gas log set. In fact, this type of arrangement is being prohibited by building codes in more jurisdictions every year due to its inherent energy waste.

[0005] The result is that most consumers are forced to install a gas-fired direct vent factory-built fireplace as manufactured and sold by numerous companies in North America. As well as finding fault with the flame appearance, consumers tend to object to the “appliance” type appearance of current gas-fired direct vent factory-built fireplace units. Louvers, vents for heat exchange and structural metal components are necessary to achieve the improved energy efficiency, however, the result is a small glass viewing area in relation to the overall front dimensions of the unit.

[0006] Louvers or vents are required below and above the combustion chamber to allow for air circulation to dissipate some the heat generated. The space below, which is relatively cool due to the inflow of convection air, also serves to house the gas control apparatus and is accessible to the user. This arrangement dictates that the “inner hearth” or base surface of the combustion chamber is always raised above the level of the outer hearth in front of the fire place.

[0007] Flame appearance is compromised by the requirement to maintain flue gas temperature below the 700 degree Fahrenheit limit set by the generic gas vent used in most installations. Without sufficiently high stack temperatures, it is not possible to provide adequate flow of combustion air to create a dynamic, “lively” flame. The result is the muted, very still flame of conventional direct vent fireplaces.

SUMMARY OF THE INVENTION

[0008] Accordingly, there is a demand for a direct vent fireplace unit that is capable of recreating the appearance of a traditional open wood fireplace with a large hearth opening and vibrant, dancing flames. The present invention provides a direct vent fireplace unit that achieves this desired appearance to avoid the external vents and louvers, muted flames and small glass viewing area of conventional direct vent units the prior art. The fireplace unit of the present invention relies on direct venting to ensure that the combustion chamber is sealed from the room.

[0009] The present invention provides a direct vent fireplace unit installable in the interior of a dwelling above a surface defining an outer hearth comprising:

[0010] an outer casing to define a cavity in the dwelling adjacent the outer hearth surface;

[0011] a combustion chamber having enclosing walls, a floor, a roof and an open front face with a combustion air inlet and an exhaust outlet communicating the combustion chamber with the exterior of the dwelling, the combustion chamber being mountable within the cavity of the outer casing such that the floor of the combustion chamber is substantially co-planar with the surface defining a hearth;

[0012] a burner element for burning fuel within the combustion chamber connectable to a fuel supply;

[0013] a controller to control the burner element; and

[0014] a transparent cover mountable over the open front of the combustion chamber to seal the combustion chamber from the interior of the dwelling.

[0015] In another aspect the present invention provides a direct vent fireplace installed in a cavity in a wall of a dwelling to have a viewable portion extending into the interior of the dwelling through an opening in the wall extending upwardly from a hearth surface comprising, in combination:

[0016] a combustion chamber having enclosing walls, a floor, a roof and an open front with a combustion air inlet and an exhaust outlet communicating the combustion chamber with the exterior of the dwelling, the open front of the combustion chamber extending across substantially the full opening in the wall;

[0017] a burner element for burning fuel within the combustion chamber connectable to a fuel supply;

[0018] a controller to control the burner element; and

[0019] a transparent cover mountable over the open front of the combustion chamber to seal the combustion chamber from the interior of the dwelling.

[0020] The present invention also provides a direct vent fireplace unit installable in a cavity within the interior of a dwelling that extends upwardly from a hearth surface, comprising:

[0021] a combustion chamber having enclosing walls, a floor, a roof and an open front face with a combustion air inlet and an exhaust outlet communicating the combustion chamber with the exterior of the dwelling, the combustion chamber being mountable within the cavity and the open front face being dimensioned to define a hearth opening that substantially fills the cavity;

[0022] a burner element for burning fuel within the combustion chamber connectable to a fuel supply;

[0023] a controller to control the burner element; and

[0024] a transparent cover mountable over the open front face of the combustion chamber to seal the combustion chamber from the interior of the dwelling.

[0025] The controller for the burner element is preferably located remote from the combustion chamber at a height convenient for the user.

[0026] The various embodiments of the direct vent fireplace unit of the present invention recreate an open, wood fire ambience with large, active flames that include an enlarged viewing region to observe the flames when compared to current direct vent fireplace units. The unit of the present invention enjoys improved heating efficiency over a traditional open fireplace while preserving the preferred active flame appearance of the open fireplace.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Aspects of the present invention are illustrated, merely by way of example, in the accompanying drawings in which:

[0028]FIG. 1 is a front view of a prior art direct vent gas fireplace to show the upper and lower louvers and the relatively small glass area available for viewing of the flames within the combustion chamber;

[0029]FIG. 2 is a schematic view of a fireplace unit according to a first embodiment of the present invention with a flat front cover;

[0030]FIG. 3 is a perspective view of a preferred embodiment of the fireplace unit of the invention a typical rough framing stage of installation;

[0031]FIG. 4 is a section view along a centre line through the fireplace unit of FIG. 3.

[0032]FIG. 5 is a section view taken along line 5-5 of FIG. 4 showing the floor of the combustion chamber with the burner element;

[0033]FIG. 5A is a detail view of the front edge of the combustion chamber as shown in FIG. 5 to illustrate the manner in which the front cover sealably engages with the combustion chamber;

[0034]FIG. 6-6B are detail views of preferred arrangements for releasably mounting the transparent cover to the open front face of combustion chamber;

[0035]FIG. 6C is a perspective view of an alternative “bay front” cover;

[0036]FIG. 6D is a perspective view of an arrangement for the open front face of the combustion chamber adapted to receive a cover with an arched top edge;

[0037]FIG. 7 is a detail view of an anchor point for releasably mounting the transparent cover to the combustion chamber; and

[0038]FIG. 8 is a perspective view of a fireplace unit with broken away sections to show details of a heat storage chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Referring to FIG. 1, there is shown a front elevation view of a conventional direct vent fireplace unit 2 installed in a cavity within a wall above a hearth surface 4. In the illustrated case, the hearth surface is the floor. Conventional unit 2 has an exposed portion that can be flush with wall 3 or protrude outwardly from the wall in a bay front arrangement. The exposed portion includes upper and lower louvers 5 and 6, respectively, mounted above and below a glass viewing area 7 that looks into a sealed combustion chamber 8 that is vented directly to the exterior of the building. Outside air is drawn through an intake duct (not shown) and mixed with gas fuel at a burner unit to create flames and heat. Combustion by-products are discharged through an exhaust duct (not shown) to the exterior of the building. The heat generated in combustion chamber 8 creates a thermal current that draws cool room air through lower louvers 6 into an area below combustion chamber 8. As the air is heated by proximity to combustion chamber 8, it rises upwardly in a cavity behind and above combustion chamber 8 and is delivered back into the room through upper louvers 5 as heated air. In general, the gas burner and controls are located in the relatively cool region below combustion chamber 8 behind louvers 6 which are removable to permit access to the controls. This arrangement requires that the combustion chamber be raised above the hearth or floor surface 4 in front of the fireplace unit. The raised combustion chamber with upper and lower louvers creates the “appliance” type appearance that is objectionable to some owners. Furthermore, this prior art arrangement, while offering good thermal efficiency approaching 75% of the heat generated in the combustion chamber being used to heat the room, requires that the air flow to the combustion chamber be carefully controlled. Air flow through the combustion chamber tends to be constrained so that heat generated within the combustion chamber is used efficiently to heat circulating room air and is not immediately exhausted through the exhaust duct. Limiting the flow of air through the combustion chamber tends to produce a small, muted flame that does not have the visual appeal of an open fireplace.

[0040] An important consideration in the design of the fireplace of the present invention is that the appearance of the combustion flame and the fireplace unit is paramount to the extent that the efficiency of heat transfer is sacrificed. It is acknowledged that the fireplace unit of the present invention has a reduced efficiency when compared to conventional direct vent units, however, the reduced efficiency is offset by an improved external appearance with an enlarged glass viewing area for observation of a large and mobile flame. The overall effect is the appearance of an open hearth wood fireplace, however, the fireplace of the present invention enjoys the advantages of direct venting and improved efficiency of approximately 40% over an open hearth arrangement.

[0041] Referring to FIG. 2, there is shown schematically an embodiment of a fireplace unit 20 according to the present invention. The unit is designed according to the principles of a direct vent fireplace in that it is installable in the interior of a dwelling with a combustion chamber 22 that is sealed from the interior and that communicates with the exterior by way of combustion air inlet 24 and an exhaust outlet 26. In FIG. 2, inlet 24 and outlet 26 are co-linear and run generally horizontally to terminate in a conventional direct vent installation 28. Alternative arrangements of the inlet and outlet are possible and will be readily apparent to one of skill in the art. In particular, co-axial venting arrangements are also common with an inner exhaust outlet being formed within an outer inlet pipe. Depending on the installation location, the vents can be run either horizontally or vertically to reach the exterior of the dwelling.

[0042] Fireplace unit 20 is preferably installed within a cavity formed in a wall 30 of the dwelling. In FIG. 2, wall 30 is shown by dashed lines in order to readily see the components of the fireplace unit normally concealed behind the wall. Combustion chamber 22 includes an open front face 32 that is visible from interior of the dwelling through an opening 33 formed in the wall. A transparent cover 34 is removably mountable over open front face 32 of the combustion chamber to seal the combustion chamber from the interior of the dwelling. Front face 32 and transparent cover 34 co-operate to define a viewable portion of the fireplace unit extending into the interior of the dwelling through wall opening 33 through which flames generated at a burner unit within the combustion chamber can be observed. Note that the open front face 32 of combustion chamber 22 extends across substantially the full opening 33 in wall 30 to provide a large viewing area without the presence of louvers. Open front face 32 of combustion chamber 22 is positioned adjacent an outer hearth 36 having an outer hearth surface 36 a that can be at any desired level with respect to the floor of the room. Often, outer hearth surface 36 a will be at or above the floor level. With the fireplace unit of the present invention, a base floor of combustion chamber 22 is positioned to be at substantially the same level as outer hearth surface 36 a with open front face 32 extending upwardly from the hearth surface and dimensioned to define a hearth opening into the combustion chamber that substantially fills the opening 33 in wall 30.

[0043] Within combustion chamber 22, there is a conventional burner element 46 (best shown in FIG. 3) for burning fuel to generate heat. Preferably, the burner element is a gas burner connectable to a gas fuel supply. A controller associated with the burner element is used to control operation of the burner element.

[0044] An outer casing 40 of sheet metal is preferably provided to define a cavity in the wall 30 of the dwelling adjacent outer hearth surface 36 a to receive combustion chamber 22. Outer casing 40 provides an exterior layer about combustion chamber 22 to isolate the combustion chamber from the flammable materials of the dwelling walls. Outer casing 40 allows the fireplace unit of the present invention to be installed according to conventional “zero-clearance” principles which permit flammable materials to be installed in close proximity to the outer casing without fear of the temperature ever rising to a sufficient level to ignite the materials.

[0045] A preferred feature of the present invention is the use of a controller that is remote from the combustion chamber. As shown in FIG. 2, a box 38 is provided remote from the combustion chamber 22 and outer casing 40 that contains a controller 41 to operate the burner element of the fireplace unit. Controller 41 communicates with burner element 46 via a flexible conduit 42. Flexible conduit 42 can formed as a single conduit containing various gas and control lines as shown in FIG. 2 or multiple conduits with each conduit housing one or more gas or control lines. FIG. 3 shows a controller 41 which employs multiple flexible conduits 42. Conduit 42 can be any desired length to permit convenient positioning of box 38 and controller 41 remote from the fireplace unit.

[0046]FIG. 3 is a detail exemplary view of a preferred embodiment of the fireplace unit of the present invention in a typical rough framing stage of installation within a dwelling. Vertical and horizontal framing members 37 and 39, respectively, are used to define a support surface for wall 30 on a floor surface 43. Framing members are positioned and dimensioned to define opening 33 in the wall into which open front face 32 of combustion chamber 22 is installed. Control box 38 connected to burner unit 46 by flexible conduit 42 is mounted to a framing member to position the box at a convenient level above floor surface 43. In the illustrated arrangement, box 38 is mounted to a vertical framing member in the same wall as the open front face 32 of combustion chamber 22. Flexible conduit 42 also permits box 38 to be mounted around a corner where it is not visible from the front of the fireplace unit. This is particularly practical when the fireplace unit is installed in a fireplace mantle extension defined by a front protruding wall and two side walls extending from a base wall. The box can be readily installed in one of the side walls so it is hidden from view.

[0047]FIG. 3 also shows an alternative location for control box 38 in a position below and in front of the combustion chamber 22. In the illustrated arrangement, alternative control box 38 with controller 41 is positioned below floor 43 which also serves as outer hearth surface 36 a. A cover (not shown) can be provided for the box that matches the appearance of hearth surface 36 a in order to hide the controls when not in use. A conduit housing a gas line and control line extends under the hearth surface 36 a to communicate the burner unit 46 within combustion chamber 22 with controller 41.

[0048] In a preferred arrangement, controller 41 comprises a control module that includes a valve to regulate the flow of fuel from the fuel supply (not shown) to the burner unit 46. In the case where box 38 is mounted externally and connected to burner unit 46 via flexible conduit 42, the valve of the control module is connected into a gas line housed in flexible conduit 42. Additional lines carry control signals from the control module to the burner unit such that the control module can be operated to ignite fuel and extinguish combustion at the burner unit. It is intended that the control module be capable of carrying out all the standard functions of a conventional control unit for direct vent fireplaces.

[0049] In the fireplace unit of FIG. 3, outer casing 40 extends rearwardly behind the framed wall for concealment behind the completed wall. Note that outer casing includes conventional standoff fins 50 to ensure that the casing is separated from wall materials a sufficient distance to prevent overheating of the materials. In this arrangement of the fireplace unit, insulated exhaust air outlet 26 extends vertically from combustion chamber 22 and through outer casing 40.

[0050]FIG. 4 is a section view taken along a vertical centre line of the fireplace unit of FIG. 3 to show details of the interior of the preferred fireplace unit. FIG. 5 is a horizontal section through the combustion chamber showing the floor of the combustion chamber. In the illustrated embodiment, combustion chamber 22 comprises a box structure of sheet metal having a generally trapezoidal cross-section in plan view (FIG. 5) with a narrowed rear wall 62 having forwardly extending side walls 60 that are angled outwardly to open front face 32. A roof 64 and a floor 66 extend between the side walls and the rear wall to the open front face. Combustion chamber 22 is mountable within the cavity defined by outer casing 40 such that side walls 60, rear wall 62 and roof 64 of the combustion chamber are spaced apart from outer casing 40 to create an air space about the combustion chamber. Floor 66 of the combustion chamber is positioned to be substantially co-planar with outer hearth surface 36 a. In this way, floor 66 of the combustion chamber defines an inner hearth surface that is co-extensive with outer hearth surface 36 a to define a combined fireplace hearth that mimics the appearance of the hearth of a conventional open wood fireplace in that the inner and outer surfaces are substantially co-planar. In the fireplace unit of the present invention, however, the transparent front cover 34 of the combustion chamber serves to seal the interior of the chamber from the interior room in order to take advantage of the direct vent features of the present invention. The generally co-planar nature of the inner and outer hearth is made possible in the present embodiment by moving the controller to a position that is external to both combustion chamber 22 and outer casing 40.

[0051] Exhaust air outlet 26 communicates with combustion chamber 22 via an opening 68 in roof 66. Combustion air inlet 24 enters the rear of outer casing 40 to deliver fresh air to the floor of the combustion chamber via opening 69 in rear wall 62. Other arrangements of inlet 24 and outlet 26 are possible and will be obvious to a person skilled in the art. For example, inlet 24 or outlet 26 may be positioned at the top or the rear of outer casing 40. On initial installation and set up of the fireplace unit, restriction plate 71 is positioned in opening 69 to adjust the size of the opening to achieve appropriate incoming fresh air flow and outgoing exhaust air flow to produce the desired combustion flame at the burner element. Movement of restriction plate 71 permits “field tuning” of the unit for different venting arrangements encountered at a particular site. For example, the longer that exhaust air outlet 26 is, the greater the volume of heated exhaust air flowing through the outlet which tends to create a larger air flow through the fireplace unit. Restriction plate 71 is positioned to provide a smaller opening to restrict the flow of inlet air into the fireplace such that the flames generated at the burner unit have the desired animated appearance without excess air flow. If exhaust air outlet 26 is shorter, restriction plate 71 can be moved to provide a larger opening to permit sufficient air flow through the combustion chamber to create the desired flame appearance. Once the unit is calibrated in this manner further adjustment is not necessary. As previously, described, the air flow through the combustion chamber is adjusted to produce large, vibrant moving flames that accurately mimic the flames of an open hearth, wood fireplace instead of the muted, stagnant flames generally associated with a conventional direct vent gas fireplace.

[0052] Baffle 74 is provided in ceiling 64 of combustion chamber 22, and is fixed to direct heated combustion air into outlet 26.

[0053] Ceramic side panels 70 and angled ceramic rear panel 72 are preferably inserted into the combustion chamber to line the interior. As is conventional, ceramic panels 70 and 72 have an exposed surface in combustion chamber 22 that has the appearance of bricks or any other desired surface. Ceramic side panels 70 are not mandatory for proper operation of the fireplace unit of the present invention.

[0054] A preferred burner unit 46 comprises a gas burner assembly 76 positioned on floor 66 of the combustion chamber. Gas burner assembly 76 is preferably incorporated into a grate assembly 78 to receive artificial logs (not shown) to create the appearance of a wood log fire. FIG. 5 is a section view taken along line 5-5 of FIG. 4 to provide a top plan view of floor 66 of the combustion chamber showing a typical gas burner assembly and grate arrangement. Gas burner assembly 76 includes a gas inlet junction 80 that connects to a gas supply via flexible conduit 42 and controller 41. Inlet junction 80 delivers gas to a generally U-shaped tube 81 with a plurality of openings to release the gas for combustion within chamber 22. It will be apparent to a person skilled in the art that other configurations of burners such as pan, tube, box burners or the like can be substituted for the illustrated burner 81.

[0055] A conventional ignition control system in the form of a pilot light assembly 82 is used to ignite the gas. Alternatively, an electronic ignition system or other ignition system can be used. Grate assembly 78 preferably comprises a plurality of interconnected grate members to retain and support artificial ceramic logs or the like. Rock wool is preferably placed over the floor of the combustion chamber about the base of the grate assembly to conceal the gas burner assembly. The rock wool glows red when heated to provide the appearance of glowing embers.

[0056] Referring again to FIGS. 4 and 5, there are show in section views through the transparent cover 34 which acts to seal the open front face 32 of combustion chamber 22. FIGS. 6 to 6B also provide detail views of portions of cover 34. Transparent cover 34 comprises an outer perimeter frame 85 adapted to sealably engage the open front face of the combustion chamber with the outer perimeter frame retaining a transparent panel 86 to permit observation of the interior of the combustion chamber. In the preferred arrangement shown in detail in FIG. 5A, open front face 32 of combustion chamber 22 is formed with an inwardly folded flat gasket flange 89 defining an outer surface about the perimeter of the open front face to which a continuous gasket 89 a is mounted. Cover 34 is positionable over the open front face of the combustion chamber such that a first portion 85 a of outer perimeter frame 85 extends inwardly past flange 89 while a second portion 85 b overlies the flange. Transparent panel 86 is thereby pressed against gasket 89 a to create a seal about the perimeter of the open front face 32 of the chamber. The opposite surface 89 b of gasket flange 89 acts as a bearing surface to support an edge of ceramic side panel 70.

[0057] Transparent panel 86 is preferably glass, but can be formed from any suitable transparent material that is able to withstand the temperatures of the combustion chamber. Ceramic glass or tempered glass are possible choices with ceramic glass being preferred.

[0058] Also formed about the perimeter of the open front face of combustion chamber 22 is a framing stop surface 88 which extends outwardly and forwardly from the sides of combustion chamber 22 as best shown in FIG. 5A. Framing stop surface 88 acts to provide a barrier for facing material about the fireplace unit to abut against. Facing material includes finishing material such as fibreboard, brick, tile, etc. Framing stop surface 88 defines a gap 88 a between the surface and those surfaces of the fireplace unit, including the combustion chamber walls and the front cover frame, that are heated during operation of the fireplace to ensure that the framing material is not heated to ignition.

[0059] Bearing in mind that the direct vent fireplace of the present invention is intended to mimic an open hearth wood fireplace, it is preferable that transparent surface of panel 86 occupies a large portion of the exposed front face of the combustion chamber to provide as large a viewing area as possible. Preferably, the transparent surface occupies an area that is at least about 85% of the area of the open front face 32 of the combustion chamber. In other words, with reference to FIG. 2, the transparent surface 86 of cover 34 extends across a significant portion of the opening 33 framed in the dwelling wall 30 through which open front face 32 of the combustion chamber extends. The overall effect is that the combustion chamber has a frontal appearance of an open hearth that extends upwardly from outer hearth surface 36 a to the edges of opening 33 in wall 30. At the same time, cover 34 including transparent panel 86 seals the interior of the combustion chamber from the interior of the room.

[0060]FIG. 6C illustrates an alternative cover 34 a sealably attachable over the open front face 32 of combustion chamber 22. In this case, cover 34 a includes a generally flat, transparent front face 86 a and a pair of separate angled transparent side panels 86 b mounted in an outer perimeter frame 85 a to define a cover having a “bay front” appearance. Cover 34 a is mounted to combustion chamber 22 in the same manner as flat cover 34 with the transparent side panels or the actual perimeter frame engaging with gasket 89. An alternative bay front arrangement employs a one-piece transparent panel with sides bent out of the plane of the front face. The one-piece panel is mounted with an outer perimeter frame which does not require the vertical frame members 87 shown in FIG. 6C.

[0061]FIG. 6D illustrates an alternative arrangement of the combustion chamber 22 of the present invention. In this case, the combustion chamber is adapted to receive a front cover 34 b having a flat transparent front face 86 b with a curved or arcuate top edge 34 c. It will be readily apparent to those skilled in the art that various configurations of the front cover are possible, and FIG. 6D provides only a representation example. In each case, the open front face 32 of combustion chamber 22 will need to be shaped to accommodate the front cover, however, any arrangement that permits releasable sealing engagement of the front cover over the open front face of the combustion chamber will permit operation of the fireplace unit of the present invention according to the principles described herein.

[0062] FIGS. 6 to 6B are detail views illustrating various clamping systems to releasably retain the outer frame 85 of cover 34 over the open front face of the combustion chamber. The clamping system is identical for bay front cover 34 a or a cover 34 b with an arcuate top edge. In each case, the clamping system includes at least one anchor point 90 mounted to the outer surface of side wall 60 of the combustion chamber and at least one latch member 92 pivotally connected to outer perimeter frame 85 of cover 34. In the illustrated arrangement anchor point 90 comprises a pin 91 engageable by a hook 93 formed on latch member 92. Latch member 92 is movable by rotation about pivot 92 a between an engaged position of anchor point 90 to interconnect the outer frame and the combustion chamber (FIG. 6 and 6A) and a disengaged position of the anchor point (FIG. 6B) to permit removal of cover 34 from the open front face of the combustion chamber. In addition, as best shown in FIG. 6D, the lower edge of front cover 34 is preferably formed with a protruding flange 200 adapted to be received in a retaining channel 220 at the front edge of the combustion chamber to define a lower joint that permits pivoting of the top edge of the cover away from the combustion chamber to relieve excess pressure while still maintaining an attachment between the cover and the chamber as will be explained in more detail below.

[0063] Preferably, the fireplace unit employs a co-operating pair of an anchor pin 91 and a latch member 92 at each side of the combustion chamber to securely anchor cover 34 in place as best shown in FIG. 2. The clamping system is positioned at the sides of the combustion chamber in the gap 96 between the combustion chamber and wall 30 where the combustion chamber extends into wall opening 33. This placement serves to substantially conceal the clamping system from view while still permitting ready access when removal of the cover is required. Alternatively, as best shown in FIG. 5A, anchor pin 91 and latch member 92 are positioned adjacent framing stop 88 within gap 88 a for concealment. Latch member 92 extends through an opening 88 b in the rear portion 88 c of framing stop 88 in order to engage pin 91.

[0064]FIG. 6 shows an arrangement in which latch member 92 includes a generally L shaped release lever 97 which extends generally forwardly from hook portion 93 toward the front of cover 34. Lever 97 also extends upwardly parallel to side of outer frame 85 of front cover 34 to terminate adjacent a top edge of the cover. A tab member 98 extends forwardly and inwardly across the top edge of front cover 34 to serve as a handle accessible from the front of the fireplace unit to move latch member 92 between the engaged and disengaged positions.

[0065]FIGS. 6A and 6B show an alternative arrangement in which latch member 92 terminates just past pivot point 92 a. FIG. 6A shows the hook portion 93 of latch member 92 in the engaged position with pin 91, while FIG. 6B shows the latch member released from pin 91, and cover 34 being pulled off the open front face 32 of the combustion chamber. This requires a pivoting and lifting motion of the cover to separate the lower joint defined by cover flange 200 seated within channel 220 of the combustion chamber (FIG. 6D). To manipulate the latch member between the engaged and disengaged positions, a special tool 100 is provided. Tool 100 includes a handle 102 for gripping by the user and a working end having two spaced arms 104 adapted to engage the end of latch member 92 adjacent pivot point 92 a. Tool 100 is dimensioned to be insertable into gap 96 between the combustion chamber and wall 30 (FIG. 2) or into gap 88 a between the combustion chamber and the framing stop 88 (FIG. 5A). Once inserted tool 100 is pivoted by the user as indicated by arrow 105 in FIG. 6B in order to pivot latch member 92 between the engaged and disengaged positions.

[0066] It is desirable that the fireplace unit of the present invention includes a pressure relief system to avoid build up of excess pressure in the combustion chamber. In conventional direct vent heating systems as illustrated in FIG. 1 that include heat exchange regions about the combustion chamber behind louvers 5 and 6, pressure relief is generally accomplished by spring biased vents that open into the heat exchange regions behind the louvers. The fireplace unit of the present invention dispenses with the louvers and a different pressure relief system is necessary. In a preferred arrangement, the pressure relief system is associated with the clamping system that retains cover 34 on the open front face of the combustion chamber. As best shown in FIG. 6, the pressure relief system comprises a biasing member 110 associated with anchor point 90 in the form of pin 91. Biasing member 110 comprises a spring 112 extending over a rod 117 between a movable stop surface 115 at one end of the rod and fixed stop surface 114 mounted via fixed bracket 116 to combustion chamber 22. Rod 117 slidably extends through a slot in stop surface 114 and through a parallel surface in bracket 116 to terminate in a bifurcated end that retains pin 91. Rod 117 and attached pin 91 are slidably retained by fixed bracket 116. By default, spring 110 applies a force on movable stop surface 115 that biases pin 91 to a position that sealably engages outer frame 85 to the open front end of combustion chamber 22 when latch member 92 and pin 91 are in the engaged position. If excess pressure develops in combustion chamber 22, the pressure will tend to pivot front cover 34 outwardly from the front face of the combustion chamber in the direction indicated by arrow 120 against the force of spring 112 to allow release of the pressure through the front of the fireplace unit. Pivoting of front cover 34 occurs about the joint defined by flange 200 at the base of cover 34 engaging in channel 220 at the lower front edge of combustion chamber 32 (FIG. 6D). This pivoting movement is permitted by sliding of rod 117 through bracket 116 so that stop surface 115 moves outwardly to compress spring 112 against stop surface 114 with corresponding sliding of pin 91 to accommodate movement of the front cover while maintaining the engagement between pin 91 and latch member 92. Once excess pressure is relieved, spring 112 will automatically act to restore pin 91 to its starting position to re-seal the front cover on the combustion chamber.

[0067] In order to accommodate the length of sliding rod 117 and movement of stop surface 115, it may be necessary to form a clearance opening 122 in the wall of outer casing 40. Such a clearance opening 122 is shown in FIG. 3. A protective cover 124 can be provided over the opening

[0068] In the event that anchor pin 91 and attached biasing member 110 requires maintenance, it is desirable that the combined assembly be removable from the combustion chamber. This is best accomplished by mounting anchor pin 91 and attached biasing member 110 to a bracket 140 that is attachable by fasteners to the side wall of combustion chamber 22. Such a removable bracket assembly is shown in detail in FIG. 7. As best shown in FIG. 6A, bracket 140 is mounted to the interior of combustion chamber side wall 60 with bracket 116 and biasing member 110 protruding through an opening 142 in the side wall to be positioned at the exterior of the combustion chamber. Anchor pin 91 and biasing member 110 are therefore accessible through the interior of the combustion chamber as exterior access is prevented by outer casing 40.

[0069]FIGS. 4 and 8 provide sectional views of a heat storage chamber 130 that can be incorporated into the outer casing 40 of the fireplace unit of the present invention. Heat storage chamber 130 comprises a region of the outer casing above the combustion chamber which is insulated by conventional insulation material 132 and through which exhaust outlet 26 passes. In FIG. 8, the front surface of outer casing 40 and the front insulation layer is cut away to provide an unobstructed view into chamber 130. Exhaust gases in the exhaust outlet heat the insulated region by conduction to create a source of stored thermal energy which would otherwise be wasted by delivery to the exterior of the dwelling with the exhaust gases.

[0070] Preferably, heat storage chamber 130 incorporates a heat distribution system for transferring thermal energy stored in the heat storage chamber to a remote location. For example, the heat distribution system may comprises at least one port 135 in the heat storage chamber having a passage 137 from the port to a location such as another room 138 in the dwelling. A fan 140 to drive heated air from the heat storage chamber to room 138 via passage 137 can be provided. Alternatively, fan 140 can be located at the outlet port in room 138 as shown by dashed lines in FIG. 8. Preferably, the fan is operated by a thermostatic control in room 138. In this way, the thermal energy generated by the fireplace unit of the present invention can be used to heat more than one room in a dwelling.

[0071] Although the present invention has been described in some detail by way of example for purposes of clarity and understanding, it will be apparent that certain changes and modifications may be practised within the scope of the appended claims. 

I claim:
 1. A direct vent fireplace unit installable in the interior of a dwelling above a surface defining an outer hearth comprising: an outer casing to define a cavity in the dwelling adjacent the outer hearth surface; a combustion chamber having enclosing walls, a floor, a roof and an open front face with a combustion air inlet and an exhaust outlet communicating the combustion chamber with the exterior of the dwelling, the combustion chamber being mountable within the cavity of the outer casing such that the floor of the combustion chamber is substantially co-planar with the surface defining the outer hearth; a burner element for burning fuel within the combustion chamber connectable to a fuel supply; a controller to control the burner element; and a transparent cover mountable over the open front of the combustion chamber to seal the combustion chamber from the interior of the dwelling.
 2. A fireplace unit as claimed in claim 1 in which the controller is positioned externally to the combustion chamber and the outer casing.
 3. A fireplace unit as claimed in claim 1 in which the burner element is a gas burner and the fuel supply is gas.
 4. A fireplace unit as claimed in claim 2 in which the controller comprises a control module that includes a valve to control flow of fuel from the fuel supply to the burner element.
 5. A fireplace unit as claimed in claim 4 in which the control module is connected to the burner element by at least one flexible line to communicate the burner element with the valve and to carry control signals from the control module.
 6. A fireplace unit as claimed in claim 1 in which the controller comprises a control module that is operable to ignite fuel and extinguish combustion at the burner element.
 7. A fireplace unit as claimed in claim 1 in which the base of the combustion chamber defines an inner hearth surface that is co-extensive with the outer hearth surface.
 8. A fireplace unit as claimed in claim 1 in which the controller is positioned below and in front of the combustion chamber.
 9. A fireplace unit as claimed in claim 1 in which the transparent cover comprises an outer frame adapted to sealably engage the open front face of the combustion chamber with the outer frame retaining a transparent panel.
 10. A fireplace unit as claimed in claim 9 in which the transparent panel is a ceramic glass panel.
 11. A fireplace unit as claimed in claim 9 in which the transparent panel is a tempered glass panel.
 12. A fireplace unit as claimed in claim 9 in which the outer frame defines a cover having a protruding front surface with angled sides.
 13. A fireplace unit as claimed in claim 9 in which the outer frame defines a cover having a generally planar front surface.
 14. A fireplace unit as claimed in claim 13 in which the outer frame includes an arcuate top edge and the open front face of the combustion chamber is shaped correspondingly.
 15. A fireplace unit as claimed in claim 9 including a clamping system to releasably retain the outer frame over the open front of the combustion chamber.
 16. A fireplace unit as claimed in claim 15 in which the clamping system comprises at least one anchor point on the combustion chamber; at least one latch member pivotally connected to the outer frame and movable between an engaged position of the at least one anchor point to interconnect the outer frame and the combustion chamber and a disengaged position of the at least one anchor point to permit removal of the transparent cover.
 17. A fireplace unit as claimed in claim 16 including a pressure relief system to avoid excess pressure in the combustion chamber.
 18. A fireplace unit as claimed in claim 17 in which the pressure relief system comprises a biasing member associated with the at least one anchor point to bias the anchor point to a position that sealably engages the outer frame to the open front of the combustion chamber by default when the latch member and the anchor point are in the engaged position and which allows movement of the outer frame away from the open front of the combustion chamber when excess pressure develops in the combustion chamber to relieve said excess pressure.
 19. A fireplace unit as claimed in claim 18 in which the biasing member comprises a spring extending between a fixed stop surface mounted to the combustion chamber and a movable stop surface connected to the anchor point.
 20. A fireplace unit as claimed in claim 17 including a joint formed between the front cover and the combustion chamber to allow pivoting of the front cover with respect to the combustion chamber to permit relief of excess pressure.
 21. A fireplace unit as claimed in claim 16 in which co-operating anchor points and latch members are positioned at each side of the combustion chamber.
 22. A fireplace unit as claimed in claim 16 in which the at least one anchor point is removably attached to the interior of the combustion chamber to protrude through a wall of the combustion chamber to the exterior of the combustion chamber.
 23. A fireplace unit as claimed in claim 16 including a tool to releasably engage and pivot the latch member between the engaged and disengaged positions.
 24. A fireplace unit as claimed in claim 9 in which the transparent surface occupies an area that is at least about 85% of the area of the open front face of the combustion chamber.
 25. A fireplace unit as claimed in claim 9 in which the transparent surface extends across substantially the same area as an opening in a wall of the dwelling communicating the cavity defined by the outer casing with the interior of the dwelling.
 26. A fireplace unit as claimed in claim 1 including a heat storage chamber associated with the outer casing.
 27. A fireplace unit as claimed in claim 26 in which the heat storage chamber comprises an insulated region of the outer casing above the combustion chamber through which the exhaust outlet passes, exhaust gases in the exhaust outlet heating the insulated region by conduction.
 28. A fireplace unit as claimed in claim 27 including a heat distribution system for transferring heat from the heat storage chamber to a remote location.
 29. A fireplace unit as claim in claim 28 in which the heat distribution system comprises at least one port in the heat storage chamber, a passage from the at least one port to the remote location and a fan to transfer heated air from the heat storage chamber to the remote location through the passage.
 30. A direct vent fireplace installed in a cavity in a wall of a dwelling to have a viewable portion extending into the interior of the dwelling through an opening in the wall extending upwardly from a hearth surface comprising, in combination: a combustion chamber having enclosing walls, a floor, a roof and an open front with a combustion air inlet and an exhaust outlet communicating the combustion chamber with the exterior of the dwelling, the open front of the combustion chamber extending across substantially the full opening in the wall; a burner element for burning fuel within the combustion chamber connectable to a fuel supply; a controller to control the burner element; and a transparent cover mountable over the open front of the combustion chamber to seal the combustion chamber from the interior of the dwelling.
 31. A direct vent fireplace as claimed in claim 30 in which the controller is positioned remote from the opening in the wall.
 32. A direct vent fireplace unit installable in a cavity within the interior of a dwelling that extends upwardly from a hearth surface, comprising: a combustion chamber having enclosing walls, a floor, a roof and an open front face with a combustion air inlet and an exhaust outlet communicating the combustion chamber with the exterior of the dwelling, the combustion chamber being mountable within the cavity and the open front face being dimensioned to define a hearth opening that substantially fills the cavity; a burner element for burning fuel within the combustion chamber connectable to a fuel supply; a controller to control the burner element; and a transparent cover mountable over the open front face of the combustion chamber to seal the combustion chamber from the interior of the dwelling.
 33. A direct vent fireplace unit as claimed in claim 32 in which the controller is external to the cavity. 